Aluminum alloy extruded material and method of manufacturing the same

ABSTRACT

An aluminum alloy extruded material having chemical composition that includes Cu by 2.5 to 3.3%, Mg by 1.3 to 2.5%, Ni by 0.50 to 1.3%, Fe by 0.50 to 1.5%, Mn by less than 0.50%, Si by 0.15 to 0.40%, Zr by 0.06 to 0.20%, and Ti by less than 0.05% in mass percentage, and the remaining part that includes Al and inevitable impurities. On a cross-section of the aluminum alloy extruded material, a grain diameter of an intermetallic compound is 20μm or less in equivalent circle diameter; density of an intermetallic compound, whose grain diameter is 0.3 to 20μm in equivalent circle diameter, is 5×10 3  piece/mm 2  or more; and, an average grain diameter of sub-crystal grains is 20μm or less in equivalent circle diameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application claims the benefit of Japanese Patent Application No. 2015-165985 filed on August 25, 2015 with the Japan Patent Office, and the entire disclosure of Japanese Patent Application No. 2015-165985 is incorporated herein by reference.

Technical Field

The present disclosure relates to an aluminum alloy extruded material and a method of manufacturing the same.

Background Art

From the standpoint of environmental preservation, there is a recent demand for improvement in fuel consumption of internal combustion engines of automobiles. Aluminum alloy materials that are applied to automobile parts, such as parts for internal combustion engines (pistons, for example) and parts for superchargers (compressor wheels, for example), are required to have strength under a high-temperature range and a creep resistance enough to endure long use under a high-temperature range to achieve a high output of internal combustion engines.

For example, Patent Document 1 suggests to control the conductivity and the average grain diameter of intermetallic compounds of an aluminum alloy material within a specified range to improve the strength of the aluminum alloy material under a high-temperature range (from 100 to 180° C.). Moreover, Patent Document 2 suggests that the content relation of Fe and Ni satisfy a specified relation to improve the strength of an aluminum alloy material under a high-temperature range (200° C. or higher).

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. H01-152237

Patent Document 2: Japanese Unexamined Patent Application Publication No. H07-242976

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Although the strength of an aluminum alloy material under a high-temperature range is discussed in the aforementioned Patent Documents 1 and 2, no discussion is given to the creep resistance under a high-temperature range. This means that, previously, there has been no sufficient discussion about the creep resistance of an aluminum alloy material under a high-temperature range.

It is desirable that one aspect of the present disclosure provides an aluminum alloy extruded material that has excellent strength and creep resistance under a high temperature and a method of manufacturing the same.

Means for Solving the Problems

One aspect of the present disclosure is an aluminum alloy extruded material having chemical composition that comprises Cu by 2.5 to 3.3%, Mg by 1.3 to 2.5%, Ni by 0.50 to 1.3%, Fe by 0.50 to 1.5%, Mn by less than 0.50%, Si by 0.15 to 0.40%, Zr by 0.06 to 0.20%, and Ti by less than 0.05% in mass percentage, and the remaining part that comprises Al and inevitable impurities. On a cross-section of the aluminum alloy extruded material, a grain diameter of an intermetallic compound is 20 μm or less in equivalent circle diameter; density of an intermetallic compound, whose grain diameter is 0.3 to 20 μm in equivalent circle diameter, is 5×10³ piece/mm² or more; and, an average grain diameter of sub-crystal grains is 20 μm or less in equivalent circle diameter.

This aluminum alloy extruded material can have an improved strength and creep resistance in a high-temperature range of 200° C. or more for example. The strength that can be improved here is not only the strength in a direction of extrusion (hereinafter optionally referred to as “L direction”) but also the strength in a direction orthogonal to the direction of extrusion (hereinafter optionally referred to as “LT direction”). The creep resistance that can be improved here is the creep resistance in the LT direction in particular. Accordingly, the aluminum alloy extruded material of the present disclosure may be applied, for example, to automobile parts such as parts for internal combustion engines and parts for superchargers that are used under a high temperature environment.

Another aspect of the present disclosure is a method of manufacturing the aforementioned aluminum alloy extruded material. The method comprises processing an ingot of an aluminum alloy that comprises the aforementioned chemical composition with homogenizing treatment at a temperature from 400 to 500° C.; then, cooling the ingot from the temperature of the homogenizing treatment to 200° C. or less at an average cooling speed of 0.01° C./s or more; then, extruding the ingot at 310 to 450° C.; then, processing an intermediate extruded material obtained by the extruding with solution treatment and quenching; then, processing the intermediate extruded material with stretch levelling at 2 to 4% strain within 48 hours after the solution treatment and quenching; and then, processing the intermediate extruded material with aging treatment at 160 to 220° C.

According to this method of manufacturing an aluminum alloy extruded material, it is possible to manufacture an aluminum alloy extruded material that has an excellent strength (strength in the L direction and the LT direction) and creep resistance (creep resistance in the LT direction in particular) under a high-temperature range of 200° C. or more for example. The aluminum alloy extruded material thus manufactured can be applied, for example, to automobile parts such as parts for internal combustion engines and parts for superchargers that are used under a high temperature environment.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present disclosure will be described hereinafter. It goes without saying that the present disclosure is not limited to the embodiments described hereinafter and may be implemented in various manners within the scope of the spirit of the present disclosure.

<Chemical Composition of Aluminum Alloy Extruded Material>

Cu: 2.5 to 3.3%

Cu contributes to an improvement in strength of an aluminum alloy extruded material under a normal temperature and under a high temperature. When Cu content is less than 2.5%, an effect of improving the strength cannot be obtained sufficiently. When the Cu content is more than 3.3%, a commencing temperature of eutectic fusion drops, and thus a decrease in a temperature of the solution treatment is required; therefore, the solid solubility of Cu in the matrix decreases, and the effect of improving the strength cannot be expected.

Mg: 1.3 to 2.5%

Mg coexists with Cu and contributes to an improvement in strength of the aluminum alloy extruded material under a normal temperature and under a high temperature. When Mg content is less than 1.3%, an effect of improving the strength is low. When the Mg content is more than 2.5%, a deformation resistance of the material in hot working processes such as extrusion increases, which results in a decrease in productivity.

Ni: 0.50 to 1.3%

Ni forms an Fe—Ni compound with Fe and improves a heat resistance of the aluminum alloy extruded material. When Ni content is less than 0.50%, an effect of improving the heat resistance cannot be obtained sufficiently. When the Ni content is more than 1.3%, Ni-based compounds, such as Al—Ni based and Al—Ni—Cu based compounds, which disperse in the matrix are formed; thus the effect of improving the heat resistance becomes low. Moreover, formation of a coarse Fe—Ni based compound increases a tendency of cracking in hot working processes such as extrusion, which results in a decrease in productivity.

Fe: 0.50 to 1.5%

Fe forms an Fe—Ni compound with Ni and improves a heat resistance of the aluminum alloy extruded material. When Fe content is less than 0.50%, an effect of improving the heat resistance cannot be obtained sufficiently. When the Fe content is more than 1.5%, Fe based compounds, such as Al—Fe based and Al—Fe—Cu based compounds, which disperse in the matrix are formed; thus the effect of improving the heat resistance becomes low.

Mn: less than 0.50%

Mn causes precipitation and dispersion of an Al—Mn—Si based compound to reduce recrystallization that occurs during the solution treatment to form fine sub-crystal grains, and thereby contributes to an improvement in strength of the aluminum alloy extruded material under a normal temperature and under a high temperature. When Mg content is 0.50% or more, a giant crystallized product is easily formed during casting, which results in a decrease in the strength.

Si: 0.15 to 0.40%

Si causes, together with Mn, precipitation of fine dispersed phase of an Al—Mn—Si based compound and increases pinning effect of dislocation to reduce coarsening of recrystallized grains during the solution treatment, and thereby helps to improve strength of the aluminum alloy extruded material. When Si content is less than 0.15%, an effect of improving the strength cannot be obtained sufficiently. When the Si content is more than 0.40%, a compound of Mg and Si is formed, which results in a decrease in the heat resistance.

Zr: 0.06 to 0.20%

Zr contributes to fining of a casted structure. Moreover, Zr causes, together with Al, fine dispersion of an Al₃Zr compound to reduce recrystallization that occurs during the solution treatment to form fine sub-crystal grains, and thereby contributes to an improvement in strength of the aluminum alloy extruded material. When Zr content is less than 0.06%, an effect of fining the casted structure and an effect of improving the strength cannot be obtained sufficiently. When the Zr content is more than 0.20%, a giant crystallized product is easily formed during casting; thus the effect of fining the casted structure and the effect of improving the strength become low.

Ti: less than 0.05%

Ti is added to stably obtain fine crystal grain structures as Zr is. Ti content should be less than 0.05%. When the Ti content is 0.05% or more, a giant Zr—Ti compound is formed during casting, which results in a decrease in the strength.

Other Elements:

Al and inevitable impurities may basically be included besides the aforementioned elements. Elements other than the aforementioned elements that are added to an aluminum alloy may usually be allowed to be included as inevitable impurities to an extent that they do not influence significantly on the characteristics of the aluminum alloy.

<Structure of Aluminum Alloy Extruded Material>

To reduce coarsening of sub-crystal grain diameters under a high temperature and achieve an excellent strength and creep resistance of the aluminum, alloy extruded material, it is necessary that crystallized products exist finely on sub-crystal grain boundaries so that a dislocation does not move easily under the high temperature. For this reason, a grain diameter of an intermetallic compound should be 20 μm or less in equivalent circle diameter (preferably 10 μm or less), and density of an intermetallic compound, whose grain diameter is 0.3 to 20 μm in equivalent circle diameter, should be 5×10³ piece/mm² or more on a cross-section of the aluminum alloy extruded material.

When the grain diameter of the intermetallic compound is more than 20 μm in equivalent circle diameter on a cross-section of the aluminum alloy extruded material, the intermetallic compound becomes the starting point of a crack, which results in a decrease in the strength of the aluminum alloy extruded material. When the density of the intermetallic compound, whose grain diameter is 0.3 to 20 μm in equivalent circle diameter, is less than 5×10³ piece/mm² on a cross-section of the aluminum alloy extruded material, precipitates on the grain boundaries become coarse and grain boundary sliding is not reduced, which result in a decrease in the heat resistance of the aluminum alloy extruded material.

To improve the strength of the aluminum alloy extruded material under a high temperature (particularly the strength in LT direction), the average grain diameter of sub-crystal grains should be 20 μm or less in equivalent circle diameter on a cross-section of the aluminum alloy extruded material. When the average grain diameter of sub-crystal grains is more than 20 μm in equivalent circle diameter on a cross-section of the aluminum alloy extruded material, the effect of improving the strength under a high temperature (particularly the strength in the LT direction) becomes low.

A cross-section of the aluminum alloy extruded material here refers to a cross-section on the aluminum alloy extruded material in a given direction. The direction of the cross-section should not be limited to any direction; for example, the cross-section may be taken in a direction parallel to the direction of extrusion, or may be taken in a direction orthogonal to the direction of extrusion. The grain diameter (in equivalent circle diameter) of the above-described intermetallic compound, the density of the intermetallic compound whose grain diameter (in equivalent circle diameter) is 0.3 to 20 μm, and the average grain diameter (in equivalent circle diameter) of sub-crystal grains can be obtained by randomly observing a region of a cross-section of the aluminum alloy extruded material, where the cross-section is taken in a given direction and the region excludes a surface layer (for example, an area from the surface to a depth of 2 to 5 mm) of the cross-section, by means of an optical microscope for example.

<Method of Manufacturing Aluminum Alloy Extruded Material>

Manufacturing of an aluminum alloy extruded material begins with melting of an aluminum alloy that comprises the aforementioned chemical composition by a conventional method and processing thus casted ingot of the aluminum alloy with homogenizing treatment at 400 to 500° C. If the treatment temperature is less than 400° C. in the homogenizing treatment, then homogenization of the structure will be insufficient. If the treatment temperature is more than 500° C., then a eutectic fusion takes place where elements are segregated.

After the homogenizing treatment, the ingot of the aluminum alloy is cooled from the homogenizing treatment temperature to a specified temperature, which is 200° C. or less, at an average cooling speed of 0.01° C./s or more. When the temperature of the homogenizing treatment is A° C. and the time required to cool the ingot from A° C. to 200° C. is B second, the average cooling speed is represented as (A° C.-200° C.)/B second. When the average cooling speed is less than 0.01° C./s (slower than 0.01° C./s), an S-phase (Al2CuMg) and/or an Fe—Ni based compound grow/grows coarsely during the cooling.

For example, if an extrusion is carried out at 450° C. or less while a coarse compound is being formed, then a dislocation introduced by the extrusion disappears in the vicinity of the coarse compound, and thus sub-crystal grain diameters become coarse. In particular, an Fe—Ni based compound remains in the final product since it does not easily dissolve during a solution treatment, which is a process after the extrusion. Since a coarse compound degrades the creep characteristics of the aluminum alloy extruded material, the cooling speed needs to be controlled so as not to produce a coarse compound during the homogenizing treatment. Accordingly, by setting the average cooling speed after the homogenizing treatment at 0.01° C./s or more to produce fine Fe—Ni based and Cu—Mg based compounds to consequently produce uniform and fine precipitates in subsequent stretch levelling and aging treatment, an aluminum alloy extruded material that has an excellent heat resistance can be obtained. Note that the “coarse compound” here refers to a compound that, for example, may keep its grain diameter in the size of 20 μm or more (in equivalent circle diameter) after the extrusion.

The cooled ingot is reheated at 310 to 450° C. and subsequently extruded at the same temperature to obtain an intermediate extruded material. Since a use of a furnace requires time to increase the temperature of the ingot and thus results in coarsening of crystallized products, it is preferable to perform extrusion of the ingot immediately after increasing its temperature by an induction heater (induction heating) or by other manners. When the temperature of extrusion is less than 310° C., a deformation resistance of the material increases and speed of extrusion decreases during the extrusion, which results in a decrease in productivity. When the temperature of extrusion is more than 450° C., dynamic recovery occurs during the extrusion, and therefore, fine sub-crystal grains cannot be obtained.

The intermediate extruded material that is obtained by the extrusion is subsequently processed with solution treatment and quenching. The temperature of the solution treatment is preferably in a temperature range that is lower by 3 to 10° C. than the commencing temperature of eutectic fusion. When the temperature of the solution treatment is higher than the aforementioned temperature range, eutectic fusion may easily occur occasionally in the material due to variations in temperatures inside the furnace. When the temperature of the solution treatment is lower than the aforementioned temperature range, solution treatment of the structure will not be performed sufficiently and thus sufficient strength may not be obtained occasionally.

The intermediate extruded material is subsequently processed with stretch levelling at 2 to 4% within 48 hours after the solution treatment and quenching. The stretch levelling is for removing residual stress and improving yield strength. Moreover, an introduction of a dislocation enables compounds to be precipitated finely in subsequent aging treatment; thus fine sub-crystal grains can be maintained in a high temperature. In particular, by finely precipitating compounds on the sub-crystal grain boundaries, movement of the dislocations is reduced and thereby an excellent high-temperature creep characteristics can be obtained.

If the time from after performing the solution treatment and quenching till performing the stretch levelling is more than 48 hours, precipitation is significantly promoted on an area where the residual stress remains. Since dislocations are prone to be introduced in a neighborhood of fine precipitates, partially promoted precipitation causes a partial introduction of dislocations by the stretch levelling, and therefore, uniform sub-crystal grains cannot be maintained afterward. If a stretch levelling amount (strain amount in the stretch levelling) is less than 2%, then effects of the above-described stretch levelling become low. If the stretch levelling amount is more than 4%, then introduced dislocations increase in excess and precipitation is promoted consequently, which results in a decrease in the high-temperature creep characteristics.

After the stretch levelling, the intermediate extruded material is subsequently processed with aging treatment at 160 to 220° C. If the temperature of the aging treatment is less than 160° C., then precipitation does not progress sufficiently. If the temperature of the aging treatment is more than 220° C., then precipitates become coarse, and thus sufficient strength cannot be obtained.

An aluminum alloy extruded material that includes the aforementioned chemical composition and the aforementioned structure can be obtained through the steps as described above.

EXAMPLES

Examples of the present disclosure will be explained hereinafter along with comparison with comparative examples to substantiate effects of the present disclosure. These examples show some of the modes of the present disclosure. The present disclosure is therefore not limited by these examples.

First, aluminum alloys (alloys A1 to A14, and B1 to B4) that include chemical composition as shown in Table 1 were casted by continuous casting to obtain billets with a diameter of 90 mm (ingots modified for extrusion). Note that, in Table 1, the remaining part besides the chemical components comprises Al and inevitable impurities, which are not shown in the table. Moreover, when the contents of the chemical components are not within the scope of the present disclosure, such contents are shown underlined.

The obtained billets were processed with the homogenizing treatment under the conditions that the treatment was conducted at 470° C. for 15 hours and cooled under the condition that the average cooling speed was 0.012° C./s, and subsequently processed with hot extrusion under the condition that the extrusion was conducted at 440° C. Through these processings, a round bar material (intermediate extruded material) with a diameter of 28 mm was obtained. The obtained round bar material was processed with the solution treatment under the conditions that the treatment was conducted at 525° C. for 2 hours, and subsequently processed with the quenching; 12 hours later, the material was processed with the stretch levelling at a strain amount of 2.4% and then processed with artificial aging treatment under the conditions that the treatment was conducted at 190° C. for 18 hours. Aluminum alloy extruded materials (hereinafter optionally referred to simply as “extruded materials”) of examples 1 to 14 and comparative examples 15 to 18 were thus prepared through the aforementioned processings.

TABLE 1 Alloy Chemical Components (in mass percentage) No. Cu Mg Ni Fe Si Mn Zr Ti Example 1 A1 3.2 2.0 1.1 1.1 0.29 0.30 0.14 0.03 2 A2 2.5 2.0 1.1 1.1 0.29 0.30 0.14 0.03 3 A3 3.0 2.4 1.1 1.1 0.29 0.30 0.14 0.03 4 A4 3.0 1.4 1.1 1.1 0.29 0.30 0.14 0.03 5 A5 3.0 2.0 1.3 1.1 0.29 0.30 0.14 0.03 6 A6 3.0 2.0 0.6 1.1 0.29 0.30 0.14 0.03 7 A7 3.0 2.0 1.1 1.3 0.29 0.30 0.14 0.03 8 A8 3.0 2.0 1.1  0.58 0.29 0.30 0.14 0.03 9 A9 3.0 2.0 1.1 1.1 0.38 0.30 0.14 0.03 10 A10 3.0 2.0 1.1 1.1 0.15 0.30 0.14 0.03 11 A11 3.0 2.0 1.1 1.1 0.29 0.45 0.14 0.03 12 A12 3.0 2.0 1.1 1.1 0.29 0.30 0.19 0.03 13 A13 3.0 2.0 1.1 1.1 0.29 0.30 0.06 0.03 14 A14 3.0 2.0 1.1 1.1 0.29 0.30 0.14 0.03 Compar- 15 B1 2.2 2.0 1.1 1.1 0.29 0.30 0.14 0.03 ative 16 B2 3.0 2.0 0.4 1.1 0.29 0.30 0.14 0.03 Example 17 B3 3.0 2.0 1.1 0.4 0.29 0.30 0.14 0.03 18 B4 3.0 2.0 1.1 1.1 0.29 0.30 0.04 0.03

On a cross-section of each prepared extruded material, the maximum grain diameter (in equivalent circle diameter) of the intermetallic compounds; density of the intermetallic compound, whose grain diameter (in equivalent circle diameter) is 0.3 to 20 μm; and, the average grain diameter (in equivalent circle diameter) of sub-crystal grains were measured. For each prepared extruded material, 0.2% yield strength (in L direction and LT direction) at room temperature and at 200° C. were measured by a tensile test, and a creep resistance (in LT direction) was evaluated by a creep rupture test. Methods of the measurements and evaluation will be explained hereinafter.

<Maximum Grain Diameter (in Equivalent Circle Diameter) and Density of Intermetallic Compounds>

To enable an observation of the structure of the extruded material in the direction of extrusion (L direction), the extruded material was cut so as to be evenly divided into two pieces in a direction parallel to the direction of extrusion (L direction) (so that the cut surfaces include the central axis of the extruded material). The cut surfaces were polished using a waterproof sandpaper, and further polished to a mirror-finish using a buff with a polish applied thereon. The central part of the cut surfaces of the extruded material (the middle point in the direction (in width direction) orthogonal to the Long direction (direction of extrusion) on the cut surface) was subsequently magnified to 200 times by an optical microscope and observed. The maximum grain diameter of the intermetallic compounds (in equivalent circle diameter) and the density of the intermetallic compound, whose grain diameter (in equivalent circle diameter) was 0.3 to 20 μm, were measured thereby.

<Average Grain Diameter (in Equivalent Circle Diameter) of Sub-Crystal Grains>

To enable an observation of the structure of the extruded material in the direction of extrusion (L direction), the extruded material was cut to be evenly divided into two pieces in the direction parallel to the direction of extrusion (L direction) (so that the cut surfaces include the central axis of the extruded material). The cut surfaces were polished using a waterproof sandpaper, and further polished to a mirror-finish using a buff with a polish applied thereon. The cut surfaces of the extruded material were then etched using Keller's reagent. The central part of the cut surfaces of the extruded material (the middle point in the direction (width direction) orthogonal to the Long direction (direction of extrusion) on the cut surface) was subsequently magnified to 200 times by an optical microscope and observed. The average grain diameter (in equivalent circle diameter) of the sub-crystal grains was measured thereby.

<0.2% Yield Strength>

With regard to the 0.2% yield strength at a room temperature, test pieces were prepared from each extruded material. Specifically, a test piece whose axis direction (Long direction) was the direction of extrusion (L direction) and a test piece whose axis direction (Long direction) was the direction orthogonal to the direction of extrusion (LT direction) were prepared for each extruded material. The test pieces were prepared to have a diameter of 5 mm at the parallel portion, the gauge length of 15 mm, and a radius of 10 mm at the shoulder portion. The test pieces were placed to a tensile test device, then tensile tests (JIS Z2241 (year 2011)) were conducted in the room temperature. In the tensile test for the LT direction, common materials are joined to both ends of an evaluation area of the test piece by friction welding to ensure the necessary length as a test piece. The 0.2% yield strength at the room temperature (in L direction and LT direction) was calculated from the result of the aforementioned tensile tests. The 0.2% yield strength at the room temperature was evaluated by using conventional values (for example, those values that are disclosed in the aforementioned Patent Document 2) as comparisons; a pass was given if the value of the 0.2% yield strength at the room temperature was 410 MPa or more.

With regard to 0.2% yield strength at 200° C., the same test pieces as those used in the aforementioned 0.2% yield strength at the room temperature were prepared from each extruded material. The test pieces were heated to 200° C. as they were placed to the tensile test device. The test pieces were maintained for 10 minutes after reaching 200° C.; then the tensile tests (JIS Z2241 (year 2011)) were conducted. The 0.2% yield strength at 200° C. (in L direction and LT direction) was calculated from the result of the aforementioned tensile tests. The 0.2% yield strength at 200° C. was evaluated by using conventional values (for example, those values that are disclosed in the aforementioned Patent Document 2) as comparisons; a pass was given if the value of the 0.2% yield strength at 200° C. was 310 MPa or more.

<Creep Resistance>

Test pieces whose axis direction (Long direction) were the direction orthogonal to the direction of extrusion (LT direction) were prepared from each extruded material in the same manner as in the aforementioned measurements of 0.2% yield strength. The test pieces were heated to 200° C. as they were placed to a creep rupture test device. The test pieces were maintained for 60 minutes after reaching 200° C.; then creep rupture tests were conducted at 200° C. Each test piece was loaded with a load of 200 MPa for 100 hours in the creep rupture tests. The load was decided to be 200 MPa based on the recent values at which high temperature properties are required. With respect to evaluations of the creep resistance (in LT direction), a pass was given if the test piece did not fracture in 100 hours with a load of 200 MPa, and a fail was given if the test piece fractured.

TABLE 2 Sub-crystal Intermetallic Compound Grains Maximum Density when Average Creep Resistance grain grain diameter grain 0.2% Yield Strength (MPa) (200 MPa/100 h) diameter is 0.3 to 20 μm diameter Room Temperature 200° C. 200° C. (μm) (×10³/mm²) (μm) L direction LT direction L direction LT direction LT direction Example 1 8.1 6.5 9.5 472 445 313 318 Pass 2 8.3 6.2 12   455 427 310 314 Pass 3 8.2 7.1 7.7 468 435 317 316 Pass 4 7.7 5.6 11   457 427 315 315 Pass 5 10 6.0 10   466 431 320 322 Pass 6 7.3 5.1 8.9 462 429 312 315 Pass 7 15 5.1 18   470 441 318 318 Pass 8 7.2 5.4 13   460 432 311 315 Pass 9 11 5.8 7.6 458 428 311 312 Pass 10 9.8 5.3 7.4 460 429 310 313 Pass 11 8.2 7.6 8.6 465 433 313 318 Pass 12 8.3 6.2 7.6 469 444 318 321 Pass 13 8.2 5.7 18   459 430 310 312 Pass 14 7.0 5.4 7.6 464 434 312 313 Pass Comparative 15 8.6 6.6 9.5 400 386 289 288 Fail Example 16 7.9 4.9 8.4 449 422 276 275 Fail 17 8.0 5.0 12   451 428 290 290 Fail 18 18 5.0 85   428 392 295 278 Fail

Table 2 shows the results of the aforementioned measurements and evaluations. When values for each item are not within the scope of the present disclosure, such values are shown underlined in Table 2.

As represented in Table 2, comparative examples 15 to 18 were not within the scope of the present disclosure; thus, these examples were given a fail in at least one of the 0.2% yield strength or the creep resistance.

Specifically, due to its low Cu content, comparative example 15 failed in the 0.2% yield strength at the room temperature (in L direction and LT direction) for not satisfying the reference value (410 MPa), failed in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value (310 MPa), and failed in the creep resistance (in LT direction).

With respect to comparative example 16, density of the intermetallic compound whose grain diameter is 0.3 to 20 μm was low due to its low Ni content; thus, comparative example 16 failed in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

Comparative example 17 failed the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value and failed in the creep resistance (in LT direction) due to its low Fe content.

Comparative example 18 recrystallized due to its low Zr content, and thus failed in the 0.2% yield strength at the room temperature (in LT direction) and in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction). The value shown in the section for the average grain diameter of sub-crystal grains for comparative example 18 in Table 2 is the average grain diameter of recrystallized grains.

Meanwhile, examples 1 to 14 passed in all of the 0.2% yield strength at the room temperature (in L direction and LT direction), the 0.2% yield strength at 200° C. (in L direction and LT direction), and the creep resistance (in LT direction), since these examples were within the scope of the present disclosure. In other words, it was revealed that the aluminum alloy extruded material of the present disclosure was excellent in the strength and the creep resistance under a high temperature.

Next, an aluminum alloy (Alloy A14: see Table 1 for its chemical composition) was casted by continuous casting to obtain a billet (356 mm in diameter). The obtained billet was processed with the homogenizing treatment under specified conditions, cooled at a specified average cooling speed, and subsequently processed with hot extrusion under specified conditions. Through these processings, a round bar material (intermediate extruded material) with a diameter of 58 mm was obtained. The obtained round bar material was processed with the solution treatment under the conditions that the treatment was conducted at 525° C. for 2 hours, and processed with the quenching; specified hours later, the material was processed with the stretch levelling at a specified strain amount and then processed with the artificial aging treatment under specified conditions. Aluminum alloy extruded materials (hereinafter optionally referred to simply as “extruded materials”) of examples 21 to 23 and comparative examples 24 to 31 were thus prepared through the aforementioned processings.

Table 3 shows temperature and duration of the homogenizing treatment, average cooling speed, extruding temperature, duration from after the solution treatment and quenching to the stretch levelling, strain amount during the stretch levelling, and temperature and duration of the aging treatment. When conditions in each processing in the method of manufacturing are not within the scope of the present disclosure, such conditions are shown underlined in Table 3.

TABLE 3 Average Time after Solution Homogenizing Cooling Extruding Treatment and Strain Amount Alloy Treatment Speed Temperature Quenching till Stretch in Stretch Aging Treatment No. (temperature/hour) (° C./s) (° C.) Levelling (h) Levelling (%) (Temperature/hour) Example 21 A14 470° C. × 15 h 0.012 440 12 2.0 190° C. × 18 h 22 A14 470° C. × 15 h 0.012 440 12 4.0 190° C. × 18 h 23 A14 470° C. × 15 h 0.012 440 12 2.5 165° C. × 48 h Comparative 24 A14 470° C. × 15 h 0.012 440 12 1.3 190° C. × 18 h Example 25 A14 470° C. × 15 h 0.012 440 12 6.0 190° C. × 12 h 26 A14 350° C. × 25 h 0.014 440 12 2.4 190° C. × 18 h 27 A14 520° C. × 15 h 0.011 440 12 2.4 190° C. × 18 h 28 A14 470° C. × 15 h 0.005 440 12 2.4 190° C. × 18 h 29 A14 470° C. × 15 h 0.013 300 x x x 30 A14 470° C. × 15 h 0.013 500 12 2.4 190° C. × 18 h 31 A14 470° C. × 15 h 0.014 440 55 2.2 190° C. × 18 h

On a cross-section of each prepared extruded material, the maximum grain diameter (in equivalent circle diameter) of the intermetallic compound; density of the intermetallic compound, whose grain diameter (in equivalent circle diameter) is 0.3 to 20μm; and the average grain diameter (in equivalent circle diameter) of sub-crystal grains were measured. For each prepared extruded material, the 0.2% yield strength (in L direction and LT direction) at the room temperature and at 200° C. were measured by the tensile test, and the creep resistance (in LT direction) was evaluated by the creep rupture test. Methods of these measurements and evaluation are the same as those explained before.

TABLE 4 Sub-crystal Intermetallic Compound Grains Maximum Density when Average Creep Resistance grain grain diameter grain 0.2% Yield Strength (MPa) (200 MPa/100 h) diameter is 0.3 to 20 μm diameter Room Temperature 200° C. 200° C. (μm) (×10³/mm²) (μm) L direction LT direction L direction LT direction LT direction Example 21 7.9 5.1 9.5 460 432 319 320 Pass 22 7.2 5.5 9.1 471 445 316 317 Pass 23 8.1 5.7 9.8 442 420 315 317 Pass Comparative 24 7.1 5.2 9.6 435 403 291 290 Fail Example 25 8.8 5.7 9.5 466 435 306 308 Fail 26 20   4.6 9.8 440 412 313 306 Fail 27 11   6.3 12   433 408 303 305 Fail 28 28   4.7 75   408 388 273 285 Fail 29 x x x x x x x x 30 15   6.2 28   444 420 310 306 Fail 31 7.3 6.8 21   437 408 312 295 Fail

Table 4 shows the results of the aforementioned measurements and evaluation. When values for each item are not within the scope of the present disclosure, such values are shown underlined in Table 4.

As represented in Table 4, methods of manufacturing in comparative examples 24 to 31 were not within the scope of the present disclosure; thus, these examples were given a fail in at least one of the 0.2% yield strength or the creep resistance.

Specifically, due to its low strain amount during the stretch levelling, comparative example 24 failed in the 0.2% yield strength at the room temperature (in LT direction) and in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

Comparative example 25 failed in the0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value and failed in the creep resistance (in LT direction) due to its excess strain amount during the stretch levelling.

With respect to comparative example 26, density of the intermetallic compound whose grain diameter is 0.3 to 20 μm was low due to its low homogenizing treatment temperature; thus, comparative example 26 failed in the 0.2% yield strength at 200° C. (in LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

Comparative example 27 failed in the 0.2% yield strength at the room temperature (in LT direction) and in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value and failed in the creep resistance (in LT direction) due to its high homogenizing treatment temperature.

With respect to comparative example 28, density of the intermetallic compound, whose grain diameter is 0.3 to 20 μm, was low and the average grain diameter of sub-crystal grains were large due to its low average cooling speed; thus, the comparative example 28 failed in the 0.2% yield strength at the room temperature (in L direction and LT direction) and in the 0.2% yield strength at 200° C. (in L direction and LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

With respect to comparative example 29, extrusion failed due to its low extruding temperature; thus, no evaluation could be conducted on an extruded material.

With respect to comparative example 30, the average grain diameter of sub-crystal grains became large due to its high extruding temperature; thus, comparative example 30 failed in the 0.2% yield strength at 200° C. (in LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

With respect to comparative example 31, the average grain diameter of sub-crystal grains became large since its duration from after the solution treatment and quenching to the stretch levelling was long; thus, comparative example 31 failed in the 0.2% yield strength at the room temperature (in LT direction) and in the 0.2% yield strength at 200° C. (in LT direction) for not satisfying the reference value, and failed in the creep resistance (in LT direction).

Meanwhile, examples 21 to 23 passed in all of the 0.2% yield strength at the room temperature (in L direction and LT direction), the 0.2% yield strength at 200° C. (in L direction and LT direction), and the creep resistance (in LT direction) since these examples were within the scope of the present disclosure. In other words, it was revealed that the method of manufacturing of an aluminum alloy extruded material in the present disclosure can provide an aluminum alloy extruded material that is excellent in the strength and the creep resistance under a high temperature. 

1. An aluminum alloy extruded material, comprising: chemical composition that comprises Cu by 2.5 to 3.3%, Mg by 1.3 to 2.5%, Ni by 0.50 to 1.3%, Fe by 0.50 to 1.5%, Mn by less than 0.50%, Si by 0.15 to 0.40%, Zr by 0.06 to 0.20%, and Ti by less than 0.05% in mass percentage, and a remaining part that comprises Al and inevitable impurities, wherein, on a cross-section of the aluminum alloy extruded material, a grain diameter of an intermetallic compound is 20 μm or less in equivalent circle diameter; density of an intermetallic compound whose grain diameter is 0.3 to 20 μm in equivalent circle diameter is 5×10³ piece/mm² or more; and, an average grain diameter of sub-crystal grains is 20 μm or less in equivalent circle diameter.
 2. A method of manufacturing the aluminum alloy extruded material according to claim 1, the method comprising: processing an ingot of an aluminum alloy that comprises the chemical composition with homogenizing treatment at a temperature from 400 to 500° C.; cooling the ingot from the temperature of the homogenizing treatment to 200° C. or less at an average cooling speed of 0.01° C./s or more; extruding the ingot at 310 to 450° C.; processing an intermediate extruded material obtained by the extruding with solution treatment and quenching; processing the intermediate extruded material with stretch levelling at 2 to 4% strain within 48 hours after the solution treatment and quenching; and, processing the intermediate extruded material with aging treatment at 160 to 220° C. 